1. Field
The present application relates generally to wireless communications, and more specifically to methods and systems for facilitating random access procedures using one or more fallback access schemes after initial access attempts have failed.
2. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, time division synchronous code division multiple access (TD-SCDMA) systems and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink (DL)) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink (UL)) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
Further, in time division synchronous code division multiple access (TD-SCDMA) systems, each TD-SCDMA frame may be divided into two subframes, each consisting of 7 time slots (TSs). In TD-SCDMA systems, a user equipment (UE) may perform a random access procedure to access the network. To facilitate the random access procedure, transmissions on the DL and UL may be aligned to avoid interference. To prevent DL signal cross interference with an uplink signal, a gap time may be used.
Generally, signals transmitted from a first base station may not interfere with signal reception at a second base station, as the signals from the first base station may be received at the second base station during the gap time, or the signal is too weak to interfere with uplink communications. However, in some cases, DL signals from a first base station may interfere with an uplink transmission slot at a second base station, and as such, may impede a UEs ability to access the second base station. Further, as a UE may select a serving base station based on the strength of DL transmissions, interference on a timeslot used for the random access procedure may repeatedly prohibit or impede a UE from access the base station.
Currently, when there is interference on a specified uplink channel used for access, access requests may be shifted into a traffic channel timeslot to avoid the interference. Such a process results on reduced uplink capacity for the system due to the fact that some uplink traffic channel timeslots are used for access transmissions. Further, in another current implementation, the gap time may be increased. For the same reasons as discussed above, an increase in gap time reduces the overall system capacity.
Therefore, there is a need for improved systems and methods for facilitating UE access procedures when access has failed due to interference on the uplink channel.